Leonid Meteor Balloon Rises Again

Meteor Balloon Rises Again

Scientists and radio amateurs team up for a live
webcast of the 2000 Leonids from the stratosphere.

November
9, 2000: On Nov. 17 and 18, 2000, space forecasters expect
a series of Leonid meteor outbursts with flurries possibly exceeding
100 shooting stars per hour. Observers in Europe, Africa, and
the eastern half of the United States and Canada are generally
favored for best viewing, but the Leonids are notoriously unpredictable.
Everyone, everywhere should remain alert for meteors during the
hours before local dawn next Friday and Saturday. [Observing
tips!]

Right: Scores of meteors rained
down over western Europe during the 1999 Leonids shower. Dazzled
observers saw brief scenes like this one, captured by A. Scott
Murrell during the 1966 Leonid storm. [credits]

Meteor watching under a crisp November sky with twinkling
stars and bright planets is an experience that's hard to beat
-- even at 3 in the morning! But if clouds, rain, or city lights
threaten to spoil your pre-dawn stargazing adventure, NASA scientists
are prepared to help.

Before dawn on Saturday, Nov. 18th, a team of astronomers
and ham radio amateurs at NASA's Marshall Space Flight Center
(MSFC) plan to launch a specially-equipped weather balloon to
monitor the Leonid meteor shower 100,000 feet above Earth's surface,
far from obscuring clouds and urban light pollution. Video from
the flight will be broadcast live on the web at LeonidsLive.com
and replays will be available less than 24 hours later.

This will be the third annual Science@NASA-sponsored
broadcast of the Leonids from the stratosphere. In 1998 and 1999
more than two million people watched live webcasts during the
meteor shower or saw replays
the morning after.

Left: The NASA/Marshall meteor balloon
recorded this Leonid fireball from a vantage point 100,000 ft
above Earth in 1998.

This year's liftoff is scheduled for 0630 Greenwich Mean Time
(0030 CST) on Saturday, Nov. 18th, from the Marshall Space Flight
Center's Atmospheric Research Facility (ARF). The balloon will
carry a sensitive low-light CCD video camera to monitor the shower
from an altitude of about 32 km (100,000 ft).

"Earth is going to pass through the outskirts of three
meteoroid debris streams from comet Tempel-Tuttle on Nov. 17th
and 18th," says Marshall astronomer Mitzi Adams. "The
last of the three stream encounters will take place at approximately
0800 GMT on Nov. 18th, just as the meteor balloon is reaching
its maximum altitude. The timing couldn't be better."

"The balloon will carry a sensitive CCD camera to record
the meteors," added Ed Myszka, an engineer and radio amateur
who built the balloon payload. "The field of view will be
about 20 degrees. That's about twice the size of the bowl of
the Big Dipper.

"We plan to downlink the video to our ground station
at the ARF as an amateur TV signal at 426.25 MHz -- that's Cable
Ready TV Channel 58. The transmission should be detectable for
several hundred miles around the launch site. Hams in the vicinity
of north Alabama and Tennessee will be able to monitor the flight
themselves. And of course the video stream will be available
for everyone on the web at LeonidsLive.com."

Sound effects during this year's flight will be provided by an
INSPIRE
VLF radio receiver, which is sensitive to radio emissions
below 10 kHz. The very low frequency (VLF) radio band is filled
with exotic-sounding signals called spherics, tweeks and whistlers.
All three are impulsive bursts caused by distant lighting. "Spherics,"
which are caused by lightning strokes within a couple of thousand
kilometers of the receiver, sound like twigs snapping or bacon
sizzling on a grill. Tweeks and whistlers are caused by more
distant lightning, and sound like brief descending musical tones.

Dennis Gallagher, a plasma physicist at the Marshall Space Flight
Center, thinks that the VLF receiver might also pick up natural
radio emissions from the Leonid meteors.

"Meteoroids produce an ionized trail as they plow through
the atmosphere," explained Gallagher. "There's a low
density wake right behind the meteoroid. Because electrons are
more mobile than protons, they move in to fill the void faster.
That could set up plasma oscillations and trigger radio emissions."

The VLF receiver was donated to the Marshall Space Flight Center
for this and future flights by the Goddard
INSPIRE program. It's been christened the "Marina receiver"
after the daughter of Flavio Gori, an Italian scientist who first
suggested flying the receiver.

Above: This time-frequency plot
(or dynamic spectrum) shows two whistlers, one at 9 minutes and
one at 12 minutes. They are caused by VLF radio emissions from
lightning strokes that travel long distances along magnetic field
lines. Other types of VLF radio emissions include tweeks, chorus,
and spherics. To learn more about the physics of these emissions,
click
here. To hear what they sound like, click
here.

Gallagher and his colleagues also plan to operate another
VLF receiver at the launch site to provide a ground reference
for comparison with data collected from the stratosphere. During
the flight, signals from the receiver will be converted to audio
sounds and transmitted along with images from the CCD video camera.
Web viewers at LeonidsLive.com will be treated to an unusual
combination of meteoritic sights and sounds.

The question of radio emissions from meteors is an intriguing
one, says Gallagher, and you don't need to send your receiver
to the stratosphere to listen in. Anyone with a VLF receiver
can monitor the Leonids on November 18 and Gallagher hopes that
INSPIRE
participants across the USA will join in the effort. The
best way to collect data is to record the output of the receiver
on a two-track audio recorder. Record the VLF signal on one track
and a WWV time signal on the other. This way VLF pulses can be
correlated with the times of bright meteors seen from your observing
site. It's also a good idea to conduct at least one observing
session a few days before or a few days after the Leonids for
comparison.

For more information about the Leonids 2000, including
predictions and observing tips, please visit LeonidsLive.com.
Daily meteor counts and information about other meteor showers
are available at SpaceWeather.com.